coa.16: Talents view no longer crashes on CoA custom classes

DataStore_Talents._GetTreeReference degrades to nil (was assert) when a custom class
(MONK, etc.) has no/partial talent reference data; Talents.lua skips background render
when GetTreeInfo returns no bg.

Altoholic/Altoholic.toc

@@ -13,7 +13,7 @@
 
 ## Author: Thaoky, Telkar-RG
 ## X-Edited-By: Exiles (Sub-Net) — florian.berthold@sub-net.at
-## Version: 3.3.002b-coa.15
+## Version: 3.3.002b-coa.16
 ## X-Category: Inventory, Tradeskill, Mail
 ## X-Localizations: enUS, frFR, zhCN, zhTW, deDE, koKR, esES, esMX, ruRU
 ## X-Website: http://wow.curse.com/downloads/wow-addons/details/altoholic.aspx

Altoholic/Frames/Talents.lua

@@ -337,6 +337,7 @@ function tns:Update(treeIndex)
 
 	-- textures are 90.625% of the original size
 	local _, bg = DS:GetTreeInfo(class, treeName)
+	if not bg then return end		-- CoA: no talent-tree background for this class (e.g. custom class with no reference data)
 	AltoholicFrameTalents_bgTopLeft:SetTexture(bg.."-TopLeft")
 	AltoholicFrameTalents_bgTopRight:SetTexture(bg.."-TopRight")
 	AltoholicFrameTalents_bgBottomLeft:SetTexture(bg.."-BottomLeft")